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(1) Field of the Invention
The present invention relates to a method for treating surfaces of substrates of molds or molded parts to remove mold release agents using continuous ultraviolet light. Ozone can be used to treat the surface in addition to the ultraviolet light. The treatment enhances surface activation, allows for surface cleaning in short time periods and increases the wetting characteristics of the surface.
(2) Description of Related Art
Surfaces of articles of manufacture which are molded or are a mold always contain undesirable compounds or additives that are used to prevent binding to the mold surface and which particularly reduce adhesion to a paint or film to the surface. Hence, surface preparation, which includes cleaning of the surfaces, of polymeric, polymer composite or metal substrates, to remove the mold release agent is carried out prior to applying protective paint films or adhesive bonding or re-use of the mold. Surface preparation determines the mechanical and durability characteristics of the layered composite created. Currently the techniques used for surface preparation are mechanical surface treatments (e.g. abrasion) solvent wash and chemical modification techniques like corona, laser plasma, flame treatment and acid etching. Each of the existing processes have shortcomings and thus, they are of limited use. Abrasion techniques are found to be time consuming, labor intensive and have the potential to damage the adherent surface. Use of organic solvents results in volatile organic chemical (VOC) emissions. Chemical techniques are costly and are of limited use with regard to treating three dimensional parts. Other methods are usually batch processes (such as plasma, acid etching) and need tight control.
Commercial washing requires multiple stages (9 to 12), chemicals and for cleaning. High pressure washers are used at each stage which consumes a lot of water which then must be purified. The economics of washing is relatively very poor.
The focused beams of lasers make it difficult to treat a large surface. U.S. Pat. No. 4,803,021 to Werth et al describes such a method. U.S. Pat. No. 4,756,765 to Woodroffe describes paint removal with surface treatment using a laser.
Plasma treatment of surfaces requires relatively expensive equipment and the plasmas are difficult to control. The surfaces are treated with any gas, e.g. vaporized water, in the plasma. Illustrative of this art are U.S. Pat. Nos. 4,717,516 to Isaka et al., 5,019,210 to Chou et al., and 5,357,005 to Buchwalter et al.
A light based process which cleans a substrate surface also creates a beneficial chemistry on the surface for adhesive bonding and paintability is described in U.S. Pat. No. 5,512,123 to Cates et al. The process involves exposing the desired substrate surface to be treated to flashlamp radiation having a wavelength of 160 to 5000 nanometers. Ozone is used with the light to increase the wetability of the surface of the substrate being treated. Surfaces of substrates such as metals, polymers, polymer composites are cleaned by exposure to the flashlamp radiation. The problem with the Cates et al process is that the surface of the substrate is heated to a relatively high temperature, particularly by radiation above 500 nanometers and requires relatively long treatment times. Related patents to Cates et al are U.S. Pat. Nos. 3,890,176 to Bolon; 4,810,434 to Caines; 4,867,796 to Asmus et al; 5,281,798 to Hamm et al and 5,500,459 to Hagemeyer et al and U.K. Patent No. 723,631 to British Cellophane. Non-patent references are: Bolon et al., xe2x80x9cUltraviolet Depolymerization of Photoresist Polymersxe2x80x9d, Polymer Engineering and Science, Vol. 12 pages 109-111 (1972). M. J. Walzak et al., xe2x80x9cUV and Ozone Treatment of Polypropylene and poly(ethylene terephthalate)xe2x80x9d, In: Polymer Surface Modification: Relevance to Adhesion, K. L. Mittal (Editor), 253-272 (1995); M. Strobel et al., xe2x80x9cA Comparison of gas-phase methods of modifying polymer surfacesxe2x80x9d, Journal of Adhesion Science and Technology, 365-383 (1995); N. Dontula et al., xe2x80x9cA study of polymer surface modification using ultraviolet radiationxe2x80x9d, Proceedings of 20th Annual Adhesion Society Meeting, Hilton Head, S.C. (1997); C. L. Weitzsacker et al., xe2x80x9cUtilizing X-ray photoelectron spectroscopy to investigate modified polymer surfacesxe2x80x9d, Proceedings of 20th Annual Adhesion Society Meeting, Hilton Head, S.C. (1997); N. Dontula et al., xe2x80x9cUltraviolet light as an adhesive bonding surface pretreatment for polymers and polymer compositesxe2x80x9d, Proceedings of ACCE""97, Detroit, Mich.; C. L. Weitzsacker et al., xe2x80x9cSurface pretreatment of plastics and polymer composites using ultraviolet lightxe2x80x9d, Proceedings of ACT""97, Detroit, Mich.; N. Dontula et al., xe2x80x9cSurface activation of polymers using ultraviolet activationxe2x80x9d, Proceedings of Society of Plastics Engineers ANTEC""97, Toronto, Canada. Haack, L. P., et al., 22nd Adhesion Soc. Meeting (Feb. 22-24, 1999).
Non-pulsed UV lamps have been used by the prior art. These are described in: xe2x80x9cExperimental Methods in Photochemistryxe2x80x9d, Chapter 7, pages 686-705 (1982). U.S. Pat. No. 5,098,618 to Zelez is illustrative of the use of these types of lamps with a low wattage input.
There is a need for development of an environmentally friendly, as well as cost effective and robust surface treatment process for removing mold release agents from surfaces.
It is therefore an object of the present invention to provide a process which is reliable and which cleans surfaces of mold release agents. It is further an object of the present invention to provide a process which is rapid and economical. These and other objects will become increasingly apparent by reference to the following description and the drawings.
The present invention relates to
A method for removing mold release agents from a surface which comprises:
exposing the surface coated with the mold release agent to continuous ultraviolet light to thereby volatilize the mold parting agent without damaging the surface.
The wattage input to the light is between about 0.1 and 20 kW to provide continuous light.
The phrase xe2x80x9cmold release agentxe2x80x9d means a thin film of any material which acts to enable a molded item to be removed from a mold. This includes lubricants and soaps used for this purpose. The agents are on the mold and on the molded product.
The phrase xe2x80x9cmolded partxe2x80x9d includes casting, injection molding, compression molding, stamping and other methods of mechanical forming.
The substance and advantages of the present invention will become increasingly apparent by reference to the following drawings and the description.